1. Technical Field
The present invention relates to a method for acquiring a color value of a device-independent color space such as CIE XYZ using a scanner that outputs a color value of a device-dependent color space such as R, G, B.
2. Description of Related Arts
In recent years, there has been an increasing demand for color print in the field of production print. Further, highly precise color reproducibility is required of production print, and in most cases an enhanced color calibration is needed to meet the requirement. Meanwhile, it has been desired that the calibration be able to be conducted in a short time without the need for high-level knowledge.
As a method for conducting the calibration in a short time, it is conceivable to acquire a color value of a device-independent color space (standard color space) such as L*a*b* using a scanner provided in a printer, for example. In order to acquire the color value of the device-independent color space, it is necessary to prepare beforehand a look-up table (hereinafter referred to as “LUT”) for converting RGB, which is outputted from the scanner which has performed the reading, to L*a*b*.
In order to acquire highly accurate L*a*b* using a scanner, it is necessary to optimize the LUT in conformity to the characteristic of the scanner since scanners are generally subjected to the device-to-device variation due to difference in characteristic among the entities. When optimizing the LUT, it was necessary to acquire a vast number of color data over the entire color space, and thus it was necessary to output patch images of many colors and to perform a color measurement of the patch images. As such, much labor and time was taken to optimize the LUT with respect to individual devices.
With regard to such problems, the image processing apparatus disclosed in Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2010-193076 (particularly, paragraphs 0037 through 0038)) is configured such that in order to reduce the number of human hours when compensating for the device-to-device variation of two sensors for reading the front and back respectively, a correcting 3D LUT is formed of a small number of patches, without the first color conversion LUT being remade which is optimized with respect to each of the devices, and correction of the first color conversion LUT is indirectly performed using the correcting 3D LUT.
However, even if the correcting 3D LUT is created merely based on the color measurement value of patches as in Patent Document 1, a highly accurate color measurement result cannot necessarily be obtained.
In particular, Patent Document 1 does not recognize such a problem that when the same-color patches in a color chart are formed of different Amounts of K, the patches are read as the same RGB data at the scanner while the colorimetric values of the colorimeter are not necessarily the same. Nor does the document refer in any way to means for solving the problem.
The present invention has been made in view of the foregoing circumstances and has for an object to provide a method for making a highly accurate color measurement taking into account of the Amount of K when a high reading accuracy cannot be obtained at a scanner, while at the same time reducing the number of man hours taken to create a scanner profile.